1. Field of the Invention
This invention relates to a tunable toolholder for suppressing vibrations caused in machining processes and, more particularly, to a tunable toolholder which utilizes a dynamic vibration absorber to suppress vibrations.
2. Description of the Prior Art
During a metal cutting operation, any vibratory motion between a cutting tool and workpiece may lead to undesirable cutting performances such as poor workpiece surface finish and out-of-tolerance finished workpieces. Furthermore, such vibration may cause the cutting tool or the machine tool to become damaged.
To reduce these vibrations, the metal removal rate can be decreased. However, this approach interferes with production and only minimally reduces the amount of vibration.
Attempts to eliminate the vibration in the boring bar may also include using a boring bar fabricated from solid carbide. Solid carbide, because of its inherently high density, reduces the amount of chatter and vibration transferred to the boring bar. However, solid carbide is extremely expensive. Furthermore, although chatter and vibration are reduced by the inherently high density of the solid carbide bar, vibration nonetheless may build to an unacceptable level. Still furthermore, solid carbide is fairly brittle and a minor impact upon the boring bar during use or setup may inadvertently damage the bar.
A further attempt to reduce vibration in boring bars includes mounting upon or within the bar a dynamic vibration absorber, such as that absorber disclosed in U.S. Pat. No. 3,774,730, which is comprised of a cylindrical mass of a high density material supported on rubber bushings. When optimally tuned, the mass oscillates in response to vibration produced in the boring bar to cancel out vibration. The absorber may be tuned to accommodate the boring bar for the speed at which the workpiece or boring bar is rotating, the length of the boring bar and the type of cutting tool connected at the end of the bar. Such an adjustment is made by longitudinally urging pressure plates at opposing ends of the cylindrical mass thereby compressing the rubber bushings against the mass which simultaneously shifts the position of the mass and alters the stiffness of the rubber bushings to change the dynamics of the cylindrical mass.
However, even with such a design available, each time the boring bar is to be used under different conditions, it must be tuned using sophisticated equipment that may or may not be available on the shop floor.
U.S. Pat. No. 3,774,730 generally identifies the design of a tunable toolholder with a dynamic vibration absorber, however, this toolholder also must be tuned each time it is used under different conditions using equipment that may or may not be available on the shop floor.
Therefore, an object of the subject invention is to provide a tunable boring bar with a dynamic absorber capable of reliably suppressing vibration, and capable of being tuned without the need to employ sophisticated equipment each time the cutting conditions change.
The invention is directed to a method for tuning a toolholder having a diameter D, wherein the toolholder may be supported on a metalworking machine at different lengths along the tool to define different length to diameter ratios. The toolholder has a shank with a longitudinal axis and a central cavity extending within the shank along the axis. The central cavity defines a cavity wall. The toolholder also has a toolholder head adapted to receive a cutting tool. The head is attached, either as a separate piece to or integral with, the shank at a tool end of the shank. Additionally, the toolholder has a tunable absorber with an absorber mass inserted within the central cavity. The mass has a first end, a second end and an elastomer support circumscribing each end. Finally the toolholder has a pressure plate at each end of the absorber mass adjacent each elastomer support, wherein at least one pressure plate is movable along the longitudinal axis to compress the elastomer supports against the absorber mass. The method is comprised of the steps of:
a) positioning the at least one movable pressure plate to a reference location in which the compression of each elastomer support is known,
b) supporting the shank on the metalworking machine at a first length L1 from the end of the shank to define a first length to diameter ratio, and
c) moving the pressure plate from the reference location to a predefined first tuned location to adjust the compression upon each elastomer support thereby minimizing vibration for the tool supported at the first length to diameter ratio.
The invention is further directed to a tunable toolholder having an outside diameter D and which may be supported on a metalworking machine at different lengths L along the tool length to define different length to diameter ratios. The toolholder has a shank with a longitudinal axis, wherein a central cavity extends within the shank along the axis and wherein the central cavity defines a cavity wall. The toolholder also has a toolholder head adapted to receive a cutting tool and attached, as a separate piece or integral, to the toolholder at a tool end. The toolholder also has a tunable absorber having an absorber mass inserted within the central cavity, wherein the mass has a first end, a second end and an elastomer support circumscribing each end of the shank. Additionally the toolholder has a pressure plate at each end of the absorber mass adjacent each elastomer support, wherein at least one pressure plate is movable along the longitudinal axis to compress the elastomer supports against the absorber mass. Additionally, the toolholder has a positioning element for displacing the movable plate from one location to another along the longitudinal axis. Finally, the toolholder has tuning indicia for indicating the position along the longitudinal axis of the at least one movable pressure plate.